1. Technical Field
The present invention relates to a tunable interference filter that selects and outputs light having a desired target wavelength from incident light, an optical module including the tunable interference filter, a photometric analyzer including the optical module, and a manufacturing method of the tunable interference filter.
2. Related Art
In related art, a light filter (tunable interference filter) in which reflection films are oppositely provided on surfaces opposed to each other of a pair of substrates is known (for example, see Patent Document 1 (JP-A-2010-139552)). In the tunable interference filter, lights are reflected between the pair of reflection films, only the light having a specific wavelength is transmitted, lights having other wavelengths are cancelled out by interferences, and thereby, the light having the specific wavelength is transmitted from incident lights.
In the tunable interference filter in Patent Document 1, the first substrate and the second substrate are oppositely provided. Further, on the surface of the first substrate that does not face the second substrate, an annular groove part is formed, and, by the formation of the groove part, a cylindrical movable part is formed in a substrate center part and a diaphragm formed coaxially with the movable part in an annular shape is formed. Further, a pair of electrodes are oppositely provided between the pair of substrates, and mirrors are oppositely provided on the surface of the movable part facing the second substrate and the second substrate. Here, by applying a voltage to the pair of electrodes, the diaphragm is curved due to electrostatic attractive force, the movable part with the mirror formed thereon moves in the substrate thickness direction, and thus, the gap between the pair of mirrors may be adjusted. Thereby, the tunable interference filter can transmit only light having a specific wavelength in response to the gap.
In the above described tunable interference filter of Patent Document 1, the diaphragm is required to be curved, and it is necessary to form the thickness dimension of the bottom surface of the groove part, i.e., the thickness dimension of the diaphragm by etching the groove part to a desired depth.
For example, in the case where the groove part is etched to the desired depth by isotropic etching, the inner side surface of the groove part is largely etched (side etching is larger), the opening edge of the groove part becomes wider, and the region of a bonded part for bonding the substrates and the region of the movable part respectively become narrower. Accordingly, in order to secure the region of the bonded part and the region of the movable part, it is necessary to use larger substrates in advance, and upsizing of the substrates is problematic.
Further, in the above described tunable interference filter of Patent Document 1, the groove part is formed only on one surface of the first substrate, and thus, the longer etching time for etching to the desired depth is problematic.